Recent times have seen the increasing significance of environmental problems on a worldwide scale and the enforcement of protection of the terrestrial biosphere as a major challenge in all sectors of industry. The field of greases is no exception to the rule, and the risk of pollution of watercourses and soils that is represented in particular by disposal into the natural environment of base oils, the main ingredients of these products, means that today progress is expected in respect of these oils, in particular in the area of biodegradability, for uses which involve the risk of external leakage of greases. At the same time, increasingly powerful machinery is subject to demands under ever more severe conditions and in addition to biodegradability, for example, their lubrication products are required to show significant improvements in performance in terms of extreme pressure and corrosion properties.
The present invention relates to a grease composition that can be used in devices which present a risk of external leakage of grease such as automobiles, construction machinery or agricultural equipment, while at the same time having a reduced environmental impact, good performance under extreme pressure and a low corrosiveness to metals or metal alloys. Surprisingly, the applicant observed that a grease composition having a combination of at least one sulfurized fatty acid ester, said ester providing a certain quantity of active sulphur at 150° C. according to standard ASTM D1662, and at least one dimercaptothiadiazole derivative, in a base oil of the polyol ester type, has very good extreme pressure properties, is not corrosive in particular to metals or metal alloys, in particular to copper, while having a reduced environmental impact.